1. Field of the Invention
The present invention relates to a damper for a drive shaft of a vehicle. More particularly, the present invention relates to a damper for a drive shaft of a vehicle having a structure by which the natural frequency is varied with temperature, thereby attenuating vibration in the overall frequency range.
2. Description of Related Art
In general, a drive shaft installed in a vehicle, which is a component for transmitting the torque of an engine to the driven wheels, includes a shaft having a predetermined length and a constant velocity joint for connection with the driven wheels.
Peripheral components such as an engine, a transmission, wheels and suspension are place near the drive shaft, so that the vibrations of the peripheral components have an effect on the drive shaft.
Thus, when the drive shaft is designed, it is based to avoid the natural frequencies of the transmission, engine, wheels and suspension.
When the drive shaft is rotated at high speed (i.e., driven at high speed), due to an additional vibration according to the rotation of the drive shaft, the drive shaft resonates with the peripheral components so that booming noise is generated. Thus, in order to avoid the resonance phenomenon to remove the booming noise, a dynamic damper is installed to the drive shaft.
Hereinafter, the function of the dynamic damper will be described in detail with reference to FIG. 1.
The drive shaft 1 may be divided into a left part LH and a right part RH with respect to the transmission. Since the drive shaft 1 leans toward one side with respect to a differential of the transmission, the length of the right part RH of the drive shaft is relatively longer than that of the left part of the drive shaft and the frequency band of the natural vibration is adjusted to a low band due to the bending phenomenon.
As the driving speed of a vehicle is increased, the frequency band is increased. When the natural frequency of the right part of the drive shaft is equal to the frequency of the vehicle (e.g., 4-cylinder: Engine C2 frequency), the resonant phenomenon occurs to generate the booming noise.
Thus, a hollow shaft has been developed and used to increase the natural frequency of the right part of the drive shaft, so that the fabrication process is complicated and the cost is increased. Therefore, in most of vehicles, a dynamic damper 2 is mounted on the drive shaft to improve the noise, vibration, and harshness (NVH) performance.
That is, the vibration of the drive shaft is attenuated at a specific frequency by using the dynamic damper, so that the resonance with the peripheral components is avoided and at the same time, the booming noise is removed, so that the durability and NVH performance of the vehicle can be improved.
For reference, the principle and property of the dynamic damper are shown in FIG. 2A. In the dynamic damper, mass m2 is added to mass m1 to reduce the amplification of vibration, so that the vibration amplification may be reduced at a target frequency (the resonant frequency of m1) based on the principle (response in using the damper in FIG. 2B) of applying an opposite phase vibration having the target frequency to reduce the amplitude. However, the natural frequency of the damper is not resistant to surrounding environment such as temperature or humidity.
As shown in FIG. 3A, the dynamic damper for a vehicle includes a steel mass and a hollow body which is molded of a rubber material such as natural rubber or styrene-butadiene rubber blend and surrounds the steel mass.
The natural frequency of the dynamic damper is varied with the mass (m) and bridge shape (shape of an interface between both ends of the steel mass and the hollow body) of the inner material and the rigidity (k) according to the matter property of the rubber material constituting the hollow body.
However, although the drive shaft on which the damper is mounted is closed to an engine so that the range of temperature variation is great, as shown in FIG. 3B, the rubber material constituting the hollow body of the damper is changed in the matter property such as hardness or elasticity according to the temperature variation.
In addition, the hardness of the dynamic damper is varied according to the variations of the bridge shape and the matter property of rubber material according to the temperature variation, so that the natural frequency is not constant, decreasing the natural frequency as shown in FIG. 3C.
That is, as the temperature is increased, although the mass of the damper is not changed, the spring constant (k) of the rubber is lowered so that the natural frequency of the dynamic damper is reduced.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.